Resist underlayer composition, and method of forming patterns using the composition

ABSTRACT

A resist underlayer composition and a method of forming patterns, the composition including a polymer including at least one of a first moiety represented by Chemical Formula 1-1 and a second moiety represented by Chemical Formula 1-2; a thermal acid generator including a salt composed of an anion of an acid and a cation of a base, the base having pKa of greater than or equal to about 7; and a solvent,

CROSS-REFERENCE TO RELATED APPLICATION

Korean Patent Application No. 10-2018-0106678, filed on Sep. 6, 2018, inthe Korean Intellectual Property Office, and entitled: “ResistUnderlayer Composition, and Method of Forming Patterns Using theComposition,” is incorporated by reference herein in its entirety.

BACKGROUND 1. Field

Embodiments relate to a resist underlayer composition and a method offorming patterns using the same.

2. Description of the Related Art

The semiconductor industry has developed to an ultra-fine techniquehaving a pattern of several to several tens of nanometer size. Suchultrafine technique uses effective lithographic techniques.

The lithographic technique may include coating a photoresist layer on asemiconductor substrate such as a silicon wafer, exposing and developingit to form a thin layer, irradiating activated radiation such asultraviolet (UV) while disposing a mask pattern having a pattern of adevice, developing the resultant to obtain a photoresist pattern,etching the substrate using the photoresist pattern as a protectivelayer to form a fine pattern corresponding to the pattern on the surfaceof the substrate.

SUMMARY

The embodiments may be realized by providing a resist underlayercomposition including a polymer including at least one of a first moietyrepresented by Chemical Formula 1-1 and a second moiety represented byChemical Formula 1-2; a thermal acid generator including a salt composedof an anion of an acid and a cation of a base, the base having pKa ofgreater than or equal to about 7; and a solvent,

wherein, in Chemical Formula 1-1 and Chemical Formula 1-2, a and f areeach independently an integer of 0 to 3, when a is 0, R¹ is hydrogen, aC1 to C30 alkyl group substituted with at least one hydroxy group, or aC1 to C30 heteroalkyl group substituted with at least one hydroxy group,when a is an integer of 1 to 3, R¹ is a hydroxy group and R⁰ is asubstituted or unsubstituted C1 to C30 alkylene group, a substituted orunsubstituted C6 to C30 arylene group, a substituted or unsubstituted C1to C30 heteroalkylene group, a substituted or unsubstituted C1 to C30heteroalkenylene group, a substituted or unsubstituted C2 to C30heteroarylene group, a substituted or unsubstituted C1 to C30 alkenylenegroup, a substituted or unsubstituted C1 to C30 alkynylene group,—(C═O)—O—, —O—, —S—, or a combination thereof, R² to R⁶ are eachindependently a substituted or unsubstituted C1 to C30 alkylene group, asubstituted or unsubstituted C6 to C30 arylene group, a substituted orunsubstituted C1 to C30 heteroalkylene group, a substituted orunsubstituted C1 to C30 heteroalkenylene group, a substituted orunsubstituted C2 to C30 heteroarylene group, a substituted orunsubstituted C1 to C30 alkenylene group, a substituted or unsubstitutedC1 to C30 alkynylene group, —(C═O)—O—, —O—, —S—, or a combinationthereof, b, c, d, and e are each independently an integer of 0 to 3,and * is a linking point.

The anion may be a non-aromatic anion.

The anion may be represented by Chemical Formula 2:

wherein, in Chemical Formula 2, R¹¹ to R¹⁵ may be each independentlyhydrogen, deuterium, a halogen, a substituted or unsubstituted C1 to C30alkyl group, or a substituted or unsubstituted C1 to C30 heteroalkylgroup, provided at least one of R¹¹ to R¹³ is a halogen, and n may be aninteger of 0 to 10.

In Chemical Formula 2, at least one of R¹¹ to R¹⁵ may be fluorine.

The cation may be represented by Chemical Formula 3:

wherein, in Chemical Formula 3, R²¹ to R²⁴ may be each independentlyhydrogen, deuterium, a substituted or unsubstituted C1 to C30 alkylgroup, or a substituted or unsubstituted C1 to C30 heteroalkyl group.

The thermal acid generator may be included in an amount of about 0.01 wt% to about 10 wt %, based on 100 wt % of the composition.

The polymer may include the first moiety represented by Chemical Formula1-1, and in Chemical Formula 1-1, R² and R³ may be each independently—(C═O)—O—, —O—, —S—, a substituted or unsubstituted C1 to C30 alkylenegroup, or a substituted or unsubstituted C1 to C30 heteroalkylene group.

The polymer may include the first moiety represented by Chemical Formula1-1, and in Chemical Formula 1-1, a may be 1, R⁰ may be —(C═O)—O—, —O—,—S—, a substituted or unsubstituted C1 to C30 alkylene group, or asubstituted or unsubstituted C1 to C30 heteroalkylene group.

The polymer may have a weight average molecular weight of about 1,000 toabout 100,000.

The polymer may be included in an amount of about 0.1 wt % to about 40wt %, based on 100 wt % of the composition.

The resist underlayer composition may further include a cross-linkingagent having two or more cross-linking sites.

The resist underlayer composition may further include a surfactant, anabsorber, a plasticizer, or a combination thereof.

The embodiments may be realized by providing a method of formingpatterns, the method including forming an etching subject layer on asubstrate, coating the resist underlayer composition according to anembodiment on the etching subject layer to form a resist underlayer,forming a photoresist pattern on the resist underlayer, and sequentiallyetching the resist underlayer and the etching subject layer using thephotoresist pattern as an etching mask.

Forming the photoresist pattern may include forming a photoresist layeron the resist underlayer, exposing the photoresist layer, and developingthe photoresist layer.

Forming the resist underlayer may further include heat-treating thecoated resist underlayer composition at a temperature of about 100° C.to about 500° C.

BRIEF DESCRIPTION OF THE DRAWINGS

Features will be apparent to those of skill in the art by describing indetail exemplary embodiments with reference to the attached drawings inwhich:

FIGS. 1 to 5 illustrate cross-sectional views of stages in a method offorming patterns using a resist underlayer composition according to anembodiment.

DETAILED DESCRIPTION

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawings; however, they may be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey exemplary implementations to those skilled in the art.

Like reference numerals refer to like elements throughout.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity and like reference numerals designate likeelements throughout the specification. It will be understood that whenan element such as a layer, film, region, or substrate is referred to asbeing “on” another element, it can be directly on the other element orintervening elements may also be present. In contrast, when an elementis referred to as being “directly on” another element, there are nointervening elements present.

As used herein, when a definition is not otherwise provided,“substituted” refers to replacement of a hydrogen atom of a compound bya substituent selected from a halogen atom (F, Br, Cl, or I), a hydroxygroup, a nitro group, a cyano group, an amino group, an azido group, anamidino group, a hydrazino group, a hydrazono group, a carbonyl group, acarbamyl group, a thiol group, an ester group, a carboxyl group or asalt thereof, a sulfonic acid group or a salt thereof, a phosphoric acidor a salt thereof, a vinyl group, a C1 to C20 alkyl group, a C2 to C20alkenyl group, a C2 to C20 alkynyl group, a C6 to C30 aryl group, a C7to C30 arylalkyl group, a C6 to C30 allyl group, a C1 to C30 alkoxygroup, a C1 to C20 heteroalkyl group, a C3 to C20 heteroarylalkyl group,a C3 to C30 cycloalkyl group, a C3 to C15 cycloalkenyl group, a C6 toC15 cycloalkynyl group, a C3 to C30 heterocycloalkyl group, and acombination thereof.

As used herein, when a definition is not otherwise provided, the term“hetero” refers to one including 1 to 10 heteroatoms selected from N, O,S, and P.

As used herein, when a definition is not otherwise provided, “*” refersto a linking point of a compound or a compound moiety. As used herein,the term “or” is not an exclusive term, e.g., “A or B” includes A, B, orA and B.

Hereinafter, a resist underlayer composition according to an embodimentis described.

A resist underlayer composition according to an embodiment may include,a thermal acid generator, and a solvent. The polymer may include, e.g.,a first moiety represented by Chemical Formula 1-1 or a second moietyrepresented by Chemical Formula 1-2 (e.g., at least one of the firstmoiety and the second moiety). The thermal acid generator may include asalt composed of an acid-derived anion (e.g., an anion of an acid) and acation derived from a base (e.g., a cation of a base) having pKa ofgreater than or equal to about 7.

In Chemical Formula 1-1 to Chemical Formula 1-2,

a and f may each independently be, e.g., an integer of 0 to 3.

In an implementation, when a is 0, R¹ may be, e.g., hydrogen, a C1 toC30 alkyl group substituted with at least one hydroxy group, or a C1 toC30 heteroalkyl group substituted with at least one hydroxy group,

In an implementation, when a is an integer of 1 to 3, R′ may be, e.g., ahydroxy group, and R⁰ may be or may include, e.g., a substituted orunsubstituted C1 to C30 alkylene group, a substituted or unsubstitutedC6 to C30 arylene group, a substituted or unsubstituted C1 to C30heteroalkylene group, a substituted or unsubstituted C1 to C30heteroalkenylene group, a substituted or unsubstituted C2 to C30heteroarylene group, a substituted or unsubstituted C1 to C30 alkenylenegroup, a substituted or unsubstituted C1 to C30 alkynylene group,—(C═O)—O— (e.g., an ester:

—O— (e.g., an ether), —S— (e.g., a thioether), or a combination thereof.

R² to R⁶ may each independently be or include, e.g., a substituted orunsubstituted C1 to C30 alkylene group, a substituted or unsubstitutedC6 to C30 arylene group, a substituted or unsubstituted C1 to C30heteroalkylene group, a substituted or unsubstituted C1 to C30heteroalkenylene group, a substituted or unsubstituted C2 to C30heteroarylene group, a substituted or unsubstituted C1 to C30 alkenylenegroup, a substituted or unsubstituted C1 to C30 alkynylene group,—(C═O)—O—, —O—, —S—, or a combination thereof.

b, c, d, and e may each independently be, e.g., an integer of 0 to 3.

* is a linking point.

The first and second moieties represented by Chemical Formula 1-1 andChemical Formula 1-2 have a structure in which a triazine backbone ispresent in the core and three oxygen atoms are linked with the triazine.Due to such a structure, a relatively high refractive index (n) and alow extinction coefficient (k) for activated radiation may be obtained.In an implementation, when the composition including the polymer isused, e.g., as a photoresist underlayer material, the composition mayhave an optimized reflectance from an etched layer with respect to alight source and thus may suppress a light interference effect and inaddition, may have high etch selectivity with a photoresist layer duringthe etching process and excellent flatness.

The first and second moieties represented by Chemical Formula 1-1 andChemical Formula 1-2 may each independently include at least one hydroxygroup and may further secure uniformity of the coating by having such astructure.

In an implementation, in Chemical Formula 1-1, when a is 0, R¹ may be,e.g., hydrogen, a C1 to C30 alkyl group substituted with at least onehydroxy group, or a C1 to C30 heteroalkyl group substituted with atleast one hydroxy group.

In an implementation, in Chemical Formula 1-1, when a is 1, R⁰ mayinclude, e.g., —(C═O)—O—, —O—, —S—, a substituted or unsubstituted C1 toC30 alkylene group (e.g., a C1 to C30 alkylene group substituted with atleast one hydroxy group), or a substituted or unsubstituted C1 to C30heteroalkylene group.

In an implementation, in Chemical Formula 1-1, R² and R³ may eachindependently include, e.g., —(C═O)—O—, —O—, or —S—.

The polymer may be stable in an organic solvent and heat, and when aresist underlayer composition including the polymer is, e.g., used as aphotoresist underlayer material, a resist underlayer formed thereof maybe minimized from delamination by the solvent or the heat during aprocess of forming a photoresist pattern or minimize generation of abyproduct such as a chemical material and the like and a thickness lossby a photoresist solvent thereon. In addition, the compound hasexcellent solubility to provide a resist underlayer having improvedcoating uniformity.

In an implementation, the polymer may be a copolymer including at leastone moiety or repeating unit of other monomers (e.g., a moiety orrepeating unit different from the first and second moieties of ChemicalFormula 1-1 and Chemical Formula 1-2.

The polymer may have a weight average molecular weight of, e.g., about1,000 to about 100,000. In an implementation, the polymer may have,e.g., a weight average molecular weight of about 1,000 to about 50,000or about 1,000 to about 20,000. When the polymer has a weight averagemolecular weight within the ranges, the amount of carbon and solubilityfor a solvent of the resist underlayer composition including the polymermay be optimized.

When the polymer is used as a material for a resist underlayer, auniform thin layer may not only be obtained without forming a pin-holeor a void and deteriorating a thickness distribution during a bakingprocess, but improved gap-fill and planarization characteristics mayalso be obtained when a lower substrate (or a layer) has a step or ispatterned.

The polymer may be included in the composition in an amount of, e.g.,greater than or equal to about 0.1 wt % or greater than or equal toabout 0.5 wt %, and less than or equal to about 40 wt %, less than orequal to about 30 wt %, or less than or equal to about 20 wt %, e.g.,about 0.1 wt % to about 40 wt % or about 0.5 wt % to about 30 wt %,based on a total weight (100 wt %) of the composition. When the polymeris included within the ranges, a thickness, a surface roughness, and aplanarization degree of the formed resist underlayer may be controlled.

In an implementation, the thermal acid generator may include a saltcomposed of an acid-derived anion and a base-derived cation. In animplementation, the thermal acid generator may be composed of the salt.In an implementation, the anion of the salt may be an anion of a basehaving a pKa of greater than or equal to about 7.

In an implementation, the anion may be a non-aromatic anion. Forexample, the anion may have no aromaticity, and it may have an effect ofimproving solubility and controlling pKa. The anion may be, e.g., ananion represented by Chemical Formula 2.

In Chemical Formula 2, R¹¹ to R¹⁵ may each independently be or include,e.g., hydrogen, deuterium, a halogen, a substituted or unsubstituted C1to C30 alkyl group, or a substituted or unsubstituted C1 to C30heteroalkyl group. In an implementation, at least one of R¹¹ to R¹³ maybe a halogen.

n may be, e.g., an integer of 0 to 10.

In an implementation, the anion may include at least one fluorine group(—F). For example, in Chemical Formula 2, at least one of R¹¹ to R¹⁵ maybe a fluorine group (—F).

In an implementation, the cation may be non-aromatic like theaforementioned anion.

In an implementation, the cation may be, e.g., represented by ChemicalFormula 3.

In Chemical Formula 3, R²¹ to R²⁴ may each independently be or include,e.g., hydrogen, deuterium, a substituted or unsubstituted C1 to C30alkyl group, or a substituted or unsubstituted C1 to C30 heteroalkylgroup.

A resist according to an embodiment may have an appropriate refractiveindex (n) and an extinction coefficient (k) sufficient to minimize aphenomenon such as a diffused reflection of an exposure light ray tophotoresist; to be coated in a uniform thickness during the coating; notto be mixed with the resist since the coated resist underlayer isdissolved in a solvent used for the coating of photoresist; and toensure etching at a faster rate than the photoresist in a dry etchingprocess for the photoresist.

The resist underlayer composition according to an embodiment may use thesalt as a thermal acid generator, e.g., the salt may be formed usinganion of a base having pKa of greater than or equal to about 7. Forexample, when the resist underlayer is formed using the resistunderlayer composition according to an embodiment, the thermal acidgenerator may generate a cross-linking of the aforementioned polymer, soas to accelerate formation of a resist underlayer, and also to maintainexcellent density and coating uniformity of the resist underlayer.

The thermal acid generator may also impart stability for an organicsolvent in the resist underlayer compositions according to anembodiment. For example, the resist underlayer composition according toan embodiment may help minimize and/or prevent dissolution of thesolvent used in photoresist coating in the formation of the pattern,while having improved storage stability.

In addition, when a resist underlayer is formed using the resistunderlayer composition including the aforementioned polymer and thermalacid generator simultaneously, the resist underlayer may have anexcellent refractive index (n) and a low extinction coefficient (k). Forexample, the resist underlayer may exhibit excellent chemical resistanceeven in a thin film state of less than or equal to about 300 Å. Usingthe resist underlayer, the photoresist pattern may effectively absorbreflected light and thus form a good pattern. For example, when thephotoresist pattern is formed using the resist underlayer, high etchselectivity and excellent pattern formability may be ensured.

The thermal acid generator may be included in an amount of, e.g.,greater than or equal to about 0.01 wt % or greater than or equal toabout 0.02 wt %, and less than or equal to about 10 wt %, less than orequal to about 5 wt %, or less than or equal to about 1 wt %. In animplementation, the thermal acid generator may include included in anamount of, e.g., about 0.01 wt % to about 10 wt % or about 0.01 wt % toabout 5 wt %, based on a total weight (100 wt %) of the composition.When the thermal acid generator is included within the ranges, formationof resist underlayer may be promoted by causing cross-linking to thepolymer at a baking temperature during bake processes of thecomposition. The resist underlayer density and the coating uniformity ofthe formed resist underlayer are also improved.

The solvent may be a suitable solvent having sufficient solubility ordispersibility or the polymer. In an implementation, the solvent mayinclude, e.g., propylene glycol, propylene glycol diacetate, methoxypropanediol, diethylene glycol, diethylene glycol butylether,tri(ethylene glycol)monomethylether, propylene glycol monomethylether,propylene glycol monomethylether acetate, cyclohexanone, ethyllactate,gamma-butyrolactone, N,N-dimethyl formamide, N,N-dimethyl acetamide,methylpyrrolidone, methylpyrrolidinone, acetylacetone, or ethyl3-ethoxypropionate.

In an implementation, the resist underlayer composition may furtherinclude a cross-linking agent.

The cross-linking agent may include, e.g., a melamine cross-linkingagent, a substituted urea cross-linking agent, or a polymercross-linking agent. In an implementation, it may be a cross-linkingagent having at least two cross-linking forming substituents, e.g.,methoxymethylated glycoluril, butoxymethylated glycoluril,methoxymethylated melamine, butoxymethylated melamine, methoxymethylatedbenzoguanamine, butoxymethylated benzoguanamine, methoxymethylatedurea,butoxymethylatedurea, methoxymethylated thiourea, butoxymethylatedthiourea, or the like.

The cross-linking agent may be a cross-linking agent having high heatresistance and may be, e.g., a compound including a cross-linkingsubstituent including an aromatic ring (for example a benzene ring, or anaphthalene ring) in the molecule. The cross-linking agent may have,e.g., two or more, three or more, or four or more cross-linking sites.

In an implementation, the resist underlayer composition may furtherinclude, e.g., at least one other polymer of an acryl resin, an epoxyresin, a novolac resin, a glycoluril resin, or a melamine resin, inaddition to the compound including the structural unit or moietyrepresented by Chemical Formula 1.

In an implementation, the resist underlayer composition may furtherinclude an additive, e.g., a surfactant, an absorber, a plasticizer, ora combination thereof.

In an implementation, the surfactant may include, e.g., an alkylbenzenesulfonate salt, an alkyl pyridinium salt, polyethylene glycol, aquaternary ammonium salt, a fluoroalkyl-based compound, or the like.

In an implementation, the plasticizer may include a suitableplasticizer. Examples of a plasticizer may include low molecularcompounds such as phthalic acid esters, adipic acid esters, phosphoricacid esters, trimellitic acid esters, citric acid esters, and the like,polyether compounds, polyester-based compounds, polyacetal compounds,and the like.

The additive may be included in an amount of, e.g., about 0.001 wt % toabout 40 wt %, based on a total weight (100 wt %) of the resistunderlayer composition. Within the ranges, solubility may be improvedwhile optical properties of the resist underlayer composition are notchanged.

According to another embodiment, a resist underlayer manufactured usingthe aforementioned resist underlayer composition may be provided. Theresist underlayer may be obtained by coating the resist underlayercomposition on, e.g., a substrate and then curing it through a heattreatment process. The resist underlayer may be, e.g., an organic thinlayer used in electronic devices such as a planarization layer, ananti-reflection coating, a sacrificial layer, or a filler.

Hereinafter, a method of forming patterns using the resist underlayercomposition is described referring to FIGS. 1 to 5.

FIGS. 1 to 5 illustrate cross-sectional views of stages in a method offorming patterns using a resist underlayer composition according to anembodiment.

Referring to FIG. 1, a subject for etching may be prepared. The etchingsubject may be a thin layer 102 formed on a semiconductor substrate 100.Hereinafter, the etching subject is the thin layer 102. A surface of thethin layer 102 may be washed to remove impurities and the like remainingthereon. The thin layer 102 may be, e.g., a silicon nitride layer, apolysilicon layer, or a silicon oxide layer.

Subsequently, the resist underlayer composition according to anembodiment (e.g., including the polymer, the thermal acid generator, andthe solvent) may be coated on the surface of the washed thin layer 102by a spin coating method.

Then, the coated composition may be dried and baked to form a resistunderlayer 104 on the thin layer 102. The baking may be performed atabout 100° C. to about 500° C., e.g., about 100° C. to about 300° C. Forexample, the resist underlayer composition may be the same as describedabove.

Referring to FIG. 2, a photoresist layer 106 may be formed by coating aphotoresist on the resist underlayer 104.

Examples of the photoresist may include a positive-type photoresistcontaining a naphthoquinone diazide compound and a novolac resin, achemically-amplified positive photoresist including an acid generatorand an alkali-soluble resin having a group capable of endowing a resinincreasing solubility in an alkali aqueous solution, and the like.

Subsequently, a substrate 100 having the photoresist layer 106 may beprimarily baked. The primary baking may be performed at about 90° C. toabout 120° C.

Referring to FIG. 3, the photoresist layer 106 may be selectivelyexposed.

Exposure of the photoresist layer 106 may be, e.g., performed bypositioning an exposure mask having a predetermined pattern on a maskstage of an exposure apparatus and aligning the exposure mask 110 on thephotoresist layer 106. Subsequently, a predetermined region of thephotoresist layer 106 on the substrate 100 may selectively react withlight passing the exposure mask by radiating light into the exposuremask 110. For example, examples of the light used during the exposuremay be a KrF excimer laser (wavelength 248 nm), an ArF excimer laser(wavelength 193 nm), EUV (extreme ultraviolet) having a wavelength of13.5 nm, and E-Beam.

An exposed region 106 a of the photoresist layer 106 may be relativelyhydrophilic or hydrophobic compared with a non-exposed region 106 b ofthe photoresist layer 106. Accordingly, the exposed region 106 a andnon-exposed region 106 b of the photoresist layer 106 may have adifferent solubility each other.

Subsequently, the substrate 100 may be secondarily baked. The secondarybaking may be performed at about 90° C. to about 150° C. The non-exposedregion 106 b of the photoresist layer may become easily soluble withrespect to a particular solvent due to the secondary baking.

Referring to FIG. 4, the non-exposed region 106 b of the photoresistlayer may be dissolved and removed by a developing solution to form aphotoresist pattern 108. For example, the non-exposed region 106 b ofthe photoresist layer may be dissolved and removed by using a developingsolution such as tetra-methyl ammonium hydroxide (TMAH) and the like tofinish the photoresist pattern 108.

Subsequently, the photoresist pattern 108 may be used as an etching maskto etch the resist underlayer. Through the etching, an organic layerpattern 112 may be formed.

The etching may be, e.g., dry etching using etching gas, and the etchinggas may be, e.g., CHF₃, CF4, Cl₂, BCl₃, or a mixed gas thereof.

Referring to FIG. 5, the photoresist pattern 108 and the organic layerpattern 112 may be used as an etching mask to etch the exposed thinlayer 102. As a result, the thin layer may be formed into a thin layerpattern 114.

Hereinafter, embodiments are described in more detail through examplesregarding synthesis of the polymer and preparation of a resistunderlayer composition including the same.

The following Examples and Comparative Examples are provided in order tohighlight characteristics of one or more embodiments, but it will beunderstood that the Examples and Comparative Examples are not to beconstrued as limiting the scope of the embodiments, nor are theComparative Examples to be construed as being outside the scope of theembodiments. Further, it will be understood that the embodiments are notlimited to the particular details described in the Examples andComparative Examples.

Synthesis of Polymer

1,3-Diallyl-5-(2-hydroxyethyl) isocyanurate (DAC-EC: 30 g, 1.0equivalent), 1,2-ethanedithiol (EDT: 11.16 g, 1.0 equivalent),azobisisobutyronitrile (AIBN: 0.389 g, 0.02 equivalent), anddimethylformamide (DMF: 166 g, for a solid content of 20%) were addedinto a 500 ml two-necked round flask connected to a condenser. Afterincreasing a temperature up to 80° C., a reaction was carried out withmonitoring a molecular weight depending upon a time using GPC.Confirming that a weight average molecular weight at 2.5 hours was3,098, a reaction solution was cooled to ambient temperature. Aftertransporting the reaction solution to a 1 L wide mouth bottle, it waswashed with 800 g of hexane three times, and subsequently washed using500 g of diethylether and 600 g of tertiary distilled water. Theobtained gum resin was completely dissolved using 80 g of THF and thenslowly dropped into 700 g of toluene which being stirred. Afterdiscarding a solvent, the residual solvent remained in the resin wasremoved using a vacuum pump to provide 29 g (final weight averagemolecular weight of 5,130, yield of 60%) of a compound. The obtainedcompound was a polymer including a structural unit of Chemical Formula1-A.

Types of Salts Salt Example 1

A salt in which an anion represented by Chemical Formula 2-1 and acation represented by Chemical Formula 3-1 formed an ionic bond anddissolved in water to have pKa=9.24, was purchased through Aldrich.

NH₄ ⁺  [Chemical Formula 3-1]

Salt Example 2

A salt in which an anion represented by Chemical Formula 2-1 and acation represented by Chemical Formula 3-2 formed an ionic bond anddissolved in water to have pKa=10.75, was purchased through Aldrich.

Salt Example 3

A salt in which an anion represented by Chemical Formula 2-1 and acation represented by Chemical Formula 3-3 formed an ionic bond anddissolved in water having pKa=10.89, was purchased through Aldrich.

Salt Example 4

A salt in which an anion represented by Chemical Formula 2-2 and acation represented by Chemical Formula 3-1 formed an ionic bond anddissolved in water to have pKa=9.24, was purchased through Aldrich.

NH₄ ⁺  [Chemical Formula 3-1]

Comparative Salt Example 1

A salt in which an anion represented by Chemical Formula 4 and a cationrepresented by Chemical Formula 3-1 formed an ionic bond was obtained.

NH₄ ⁺  [Chemical Formula 3-1]

Comparative Salt Example 2

A salt in which an anion represented by Chemical Formula 4 and a cationrepresented by Chemical Formula 5 formed an ionic bond and dissolved inwater to have pKa=5.25, was purchased through Aldrich.

Comparative Salt Example 3

Without forming a salt, a compound (pKa=−2.8 when dissolved in water)represented by Chemical Formula 6 was used.

Preparation of Resist Underlayer Composition Example 1

A polymer represented by Chemical Formula 1-1, PL1174 manufactured byTCI as a cross-linking agent (in an amount of 15 wt % based on totalweight, 100 wt %, of the polymer) and the salt of Salt Example 1 (in anamount of 3 wt % based on total weight, 100 wt %, of the polymer) weredissolved in a mixed solvent (mixing weight ratio=1:1) of propyleneglycol monomethylether and ethyl lactate, and then stirred for 6 hoursto provide a resist underlayer composition.

An amount of the mixed solvent was adjusted to provide a solid contentof the polymer at 1 wt %, based on a total weight (100 wt %) of theobtained resist underlayer composition.

Example 2 to Example 4

Each resist underlayer composition was prepared in accordance with thesame procedure as in Example 1, except that each salt of Salt Examples 2to 4 was used instead of the salt used in Example 1.

Comparative Example 1 to Comparative Example 3

Each resist underlayer composition was prepared in accordance with thesame procedure as in Example 1, except that the salt or the compositionof each of Comparative Salt Examples 1 to 3 was used instead of the saltused in Example 1.

Evaluation 1: Evaluation of Layer Density

The compositions of Examples 1 to 4 and Comparative Examples 1 to 3 wereeach taken in 2 mL samples, coated on a 4-inch wafer, and then a spincoating was performed at 1,500 rpm for 20 seconds using an auto trackACT8 (manufactured by TEL). Then it was cured at 210° C. for 90 secondsto provide a resist underlayer having a thickness of 30 nm. Each resistunderlayer was performed with a measurement through a XRR method tomeasure a density of a resist underlayer based on a threshold angle.X'pert PRO MPD (manufactured by Panalytical) was used as a measuringequipment.

The results are shown in Table 1.

TABLE 1 Layer density (dyne/cm²) Example 1 1.31 Example 2 1.31 Example 31.31 Example 4 1.31 Comparative Example 1 1.29 Comparative Example 21.29 Comparative Example 3 1.28

Referring to Table 1, it may be that the resist underlayer formed fromthe compositions of Examples 1 to 4 exhibited excellent layer density,compared with Comparative Examples 1 to 3.

Evaluation 2: Evaluation of Coating Uniformity

Each resist underlayer obtained from Evaluation 1 was measured for a 51point thickness in the horizontal axis, and the coating uniformitythereof was compared. The thickness was measured by Opti-2600(manufactured by Thermawave) employing ellipsometry, and the results areshown in Table 2.

In Table 2, smaller coating uniformities (%) are better.

TABLE 2 Coating uniformity (%) Example 1 0.7 Example 2 0.7 Example 3 0.8Example 4 0.7 Comparative Example 1 0.8 Comparative Example 2 0.9Comparative Example 3 1.1

Referring to Table 2, it may be that resist underlayer compositions ofExamples 1 to 4 had more excellent coating uniformity than the resistunderlayer compositions of Comparative Examples 1 to 3.

Evaluation 3: Evaluation of Storage Stability

Resist underlayer compositions of Examples 1 to 4 and ComparativeExamples 1 to 3 were stored at 40° C. for 1 month, and the morphologyand the precipitation degree were each monitored by a gel transmissionchromatography to compare the storage stability, and the results areshown in Table 3.

In Table 3, the storage stability is better as there is no graph changein the gel permeation chromatography and no precipitation.

TABLE 3 Graph change in gel permeation chromatography PrecipitationExample 1 X not generated Example 2 X not generated Example 3 X notgenerated Example 4 X not generated Comparative Example 1 ◯ notgenerated Comparative Example 2 ◯ generated Comparative Example 3 ◯generated

Referring to Table 3, the resist underlayer compositions according toExamples 1 to 4 exhibited excellent storage stability, compared with theresist underlayer compositions according to Comparative Examples 1 to 3.

By way of summation and review, as technology for manufacturing anultra-fine pattern, an activated radiation having a short wavelengthsuch as an i-line (365 nm), a KrF excimer laser (wavelength of 248 nm),an ArF excimer laser (wavelength of 193 nm), and the like may be usedfor exposure of a photoresist. The activated radiation may cause adiffused reflection from a semiconductor substrate, a standing wave, orthe like. A resist underlayer having optimal reflectance may be includedbetween the photoresist and the semiconductor substrate.

A high energy ray such as EUV (extreme ultraviolet; a wavelength of 13.5nm), an E-beam (electron beam), and the like as a light source formanufacturing the fine pattern in addition to the activated radiationmay be used, and the light source has no reflection from the substrate.Adherence of the resist to the lower layer may be improved to improve acollapse of the pattern. In addition, etch selectivity and chemicalresistance of the resist underlayer may be improved, and issues causedby the light source may be considered.

One or more embodiments may provide a photoresist underlayer compositionformed between a semiconductor substrate and a photoresist layer, and amethod of forming photoresist patterns using the undercoat layer.

One or more embodiments may provide a resist underlayer compositionhaving optimal reflectance in a predetermined wavelength andsimultaneously, improved coating properties, storage stability, andchemical resistance.

Example embodiments have been disclosed herein, and although specificterms are employed, they are used and are to be interpreted in a genericand descriptive sense only and not for purpose of limitation. In someinstances, as would be apparent to one of ordinary skill in the art asof the filing of the present application, features, characteristics,and/or elements described in connection with a particular embodiment maybe used singly or in combination with features, characteristics, and/orelements described in connection with other embodiments unless otherwisespecifically indicated. Accordingly, it will be understood by those ofskill in the art that various changes in form and details may be madewithout departing from the spirit and scope of the present invention asset forth in the following claims.

What is claimed is:
 1. A resist underlayer composition, comprising: apolymer including at least one of a first moiety represented by ChemicalFormula 1-1 and a second moiety represented by Chemical Formula 1-2; athermal acid generator including a salt composed of an anion of an acidand a cation of a base, the base having pKa of greater than or equal toabout 7; and a solvent,

wherein, in Chemical Formula 1-1 and Chemical Formula 1-2, a and f areeach independently an integer of 0 to 3, when a is 0, R¹ is hydrogen, aC1 to C30 alkyl group substituted with at least one hydroxy group, or aC1 to C30 heteroalkyl group substituted with at least one hydroxy group,when a is an integer of 1 to 3, R¹ is a hydroxy group and R⁰ is asubstituted or unsubstituted C1 to C30 alkylene group, a substituted orunsubstituted C6 to C30 arylene group, a substituted or unsubstituted C1to C30 heteroalkylene group, a substituted or unsubstituted C1 to C30heteroalkenylene group, a substituted or unsubstituted C2 to C30heteroarylene group, a substituted or unsubstituted C2 to C30 alkenylenegroup, a substituted or unsubstituted C2 to C30 alkynylene group,—(C═O)—O—, —O—, —S—, or a combination thereof, R² to R⁶ are eachindependently a substituted or unsubstituted C1 to C30 alkylene group, asubstituted or unsubstituted C6 to C30 arylene group, a substituted orunsubstituted C1 to C30 heteroalkylene group, a substituted orunsubstituted C1 to C30 heteroalkenylene group, a substituted orunsubstituted C2 to C30 heteroarylene group, a substituted orunsubstituted C2 to C30 alkenylene group, a substituted or unsubstitutedC2 to C30 alkynylene group, —(C═O)—O—, —O—, —S—, or a combinationthereof, provided that R⁴ to R⁶ do not comprise —O—, and at least one ofR⁴ to R⁶ comprises —S—, b and c are each independently an integer of 0to 3, d and e are each independently an integer of 1 to 3, and * is alinking point.
 2. The resist underlayer composition as claimed in claim1, wherein the anion is a non-aromatic anion.
 3. The resist underlayercomposition as claimed in claim 2, wherein the anion is represented byChemical Formula 2:

wherein, in Chemical Formula 2, R¹¹ to R¹⁵ are each independentlyhydrogen, deuterium, a halogen, a substituted or unsubstituted C1 to C30alkyl group, or a substituted or unsubstituted C1 to C30 heteroalkylgroup, provided at least one of R¹¹ to R¹³ is a halogen, and n is aninteger of 0 to
 10. 4. The resist underlayer composition as claimed inclaim 3, wherein in Chemical Formula 2, at least one of R¹¹ to R¹⁵ isfluorine.
 5. The resist underlayer composition as claimed in claim 1,wherein the cation is represented by Chemical Formula 3:

wherein, in Chemical Formula 3, R²¹ to R²⁴ are each independentlyhydrogen, deuterium, a substituted or unsubstituted C1 to C30 alkylgroup, or a substituted or unsubstituted C1 to C30 heteroalkyl group. 6.The resist underlayer composition as claimed in claim 1, wherein thethermal acid generator is included in an amount of about 0.01 wt % toabout 10 wt %, based on 100 wt % of the composition.
 7. The resistunderlayer composition as claimed in claim 1, wherein: the polymerincludes the first moiety represented by Chemical Formula 1-1, and inChemical Formula 1-1, R² and R³ are each independently —(C═O)—O—, —O—,—S—, a substituted or unsubstituted C1 to C30 alkylene group, or asubstituted or unsubstituted C1 to C30 heteroalkylene group.
 8. Theresist underlayer composition as claimed in claim 1, wherein: thepolymer includes the first moiety represented by Chemical Formula 1-1,and in Chemical Formula 1-1, a is 1, R⁰ is —(C═O)—O—, —O—, —S—, asubstituted or unsubstituted C1 to C30 alkylene group, or a substitutedor unsubstituted C1 to C30 heteroalkylene group.
 9. The resistunderlayer composition as claimed in claim 1, wherein the polymer has aweight average molecular weight of about 1,000 to about 100,000.
 10. Theresist underlayer composition as claimed in claim 1, wherein the polymeris included in an amount of about 0.1 wt % to about 40 wt %, based on100 wt % of the composition.
 11. The resist underlayer composition asclaimed in claim 1, further comprising a cross-linking agent having twoor more cross-linking sites.
 12. The resist underlayer composition asclaimed in claim 1, further comprising a surfactant, an absorber, aplasticizer, or a combination thereof.
 13. The resist underlayercomposition as claimed in claim 1, wherein the polymer has a weightaverage molecular weight of about 5,000 to about 100,000.
 14. The resistunderlayer composition as claimed in claim 1, wherein the polymerincludes the second moiety represented by Chemical Formula 1-2.